Dependencies

Listing an app as a dependency of the monolith gets you most of the way. An App Router route is only symlinked, so Turbopack resolves it at its real path inside the app and finds the app's own node_modules from there. It is not quite enough, for two reasons.

Pages Router files are copied. Their real path is inside the monolith, so the app's node_modules is no longer above them and nothing they import resolves.

TypeScript resolves from where the file sits in the monolith, not from the symlink's target, so even App Router routes fail to type check against the app's dependencies. Turbopack compiles them happily, which makes this easy to miss — the build gets all the way to Running TypeScript before anything complains.

Merging

fg-monolith merge-package-json reads what the route trees actually import and folds just those into the monolith's package.json, resolving conflicting ranges by semver rather than by whichever app happens to be last.

fg-monolith merge-package-json           # writes package.json
fg-monolith merge-package-json --check   # exits 1 if out of date, for CI
fg-monolith merge-package-json --all     # every dependency, not just imports

Run it before installing. The app list comes from the monolith's own next.config.*, so it stays the single source of truth.

What gets taken

Only direct imports in app/ and pages/. Anything an app reaches through its own package name resolves via the monolith's link to the app and carries on from there, so it needs nothing.

• Relative imports and node builtins are skipped.
• A subpath import is reduced to its package: @scope/design/components/Button asks for @scope/design.
• require() and dynamic import() count.
• A @types/ package is taken along with whatever it describes.
• Workspace and link ranges are skipped, since those are linked rather than installed.

In the Fair Garden repository that is 15 packages rather than 24. Scanning leaves behind the app's own lint plugins, and the dependencies of a proxy the monolith does not mount.

Use --all if something outside the route trees is resolved from the monolith.

Other commands

fg-monolith link       # mount without starting Next
fg-monolith list       # print the apps and where they resolved to

link takes --strategy and both take --cwd.